drm/i915: Fix LVDS panel fitting on Arrandale

Arrandale has new window based method for panel fitting.
This one enables full screen aspect scaling on LVDS. It fixes
standard mode display failure on LVDS for Arrandale.

Cc: Stable Team <stable@kernel.org>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>